1. Field of the Invention
The present invention relates to an image heating apparatus which is used for an image forming apparatus such as an electro photographic device and an electrostatic recording device and which heats an image formed on a sheet.
2. Description of the Related Art
In an image forming apparatus such as the electro photographic device and the electrostatic recording device, a toner image is formed on the sheet, the toner image is heated, pressurized and fixed, thereby forming an image. As an apparatus which carries out such a fixing operation, there is an apparatus which forms a fixing nip by a heating member and a pressing member which pressurizes the heating member, and the fixing operation is carried out while nipping and conveying the sheet between the heating member and the pressing member.
In such a fixing apparatus (image heating apparatus), there is an apparatus in which a conveying roller behind a fixing nip can be separated from a fixing apparatus so that a user, a service man or an operator can perform maintenance or remove a remaining paper sheet (see Japanese Patent Application Laid-open No. 4-316076).
Conventionally, as shown in FIG. 14, after a pullout unit 1092 fixed to a pullout rail 1091 is pulled out from a casing of an image forming apparatus 1001, maintenance of a fixing apparatus 1005 placed on the pullout unit 1092 is carried out.
As shown in FIG. 15A, the fixing apparatus 1005 includes a fixing roller 1071 and a pressing belt 1731 which forms a nip portion between the pressing belt 1731 and the fixing roller 1071. In the fixing apparatus 1005, a separation projection 1800 and a division plate 1817 are provided adjacent to the pressing belt 1731 and the fixing roller 1071.
An open/close unit 1081 includes a pair of rotate arms 1085 which respectively holds both ends of the separation projection 1800, the division plate 1817, and a pair of conveying rollers 1082 (only one ends thereof are illustrated in FIG. 15). The separation projection 1800 is urged against the pressing belt 1731 by a tension spring in a state where the pressing belt 1731 abuts against the fixing roller 1071 for separating a sheet from the pressing belt 1731.
As shown in FIG. 15B, the open/close unit 1081 can rotate around a rotate shaft 1819 in a direction separating from the fixing roller 1071 and the pressing belt 1731 (direction of the arrow A′). Thus, the separation projection 1800, the division plate 1817 and the pair of conveying rollers 1082 can retract from the fixing roller 1071 and the pressing belt 1731 in the direction of the arrow C′.
In such an apparatus, when accessing the fixing apparatus for maintenance or jam recovery at the fixing portion, the pressing belt 1731 is separated from the fixing roller 1071 and the pressure is released. Then, the open/close unit 1081 is rotated to form a space for maintenance so that a user or an operator can access the fixing apparatus.
However, a power supply is suddenly shut off due to a power failure or trouble in a state where the fixing roller 1071 and the pressing belt 1731 are pressurized, or the fixing roller 1071 and the pressing belt 1731 are not separated from each other due to malfunction and the operation is stopped in the pressurized state in some cases.
Conventionally, an operator can operate the open/close unit 1081 even in a state where the pressing belt 1731 and the separation projection 1800 are in abutment against each other. Thus, in the conventional apparatus, there is a danger that the separation projection 1800 pressed against the pressing belt 1731 scrapes against the pressing belt 1731 excessively at the time of opening operation of the open/close unit 1081.
If the pressing belt 1731 scrapes against the separation projection 1800 excessively, a flaw which can not be negligible is generated on a surface of the pressing belt 1731. There is a danger that such a phenomenon occurs even when the separation projection and the pressing belt are disposed at a slight distance away from each other.
If such a flaw is generated in the pressing belt, endurance and lifetime of the pressing belt are deteriorated. There is an adverse possibility that image failure is generated. In particular, when images are to be formed on both surfaces of a sheet, if an image formed on a first surface of the sheet comes into contact with the pressing belt 1731, a flaw generated on the pressing belt 1731 is transferred to that image. With this, uneven brightness (gloss unevenness) is generated on the image of the first surface of the sheet, and the image quality is degraded. This gloss unevenness appears seriously especially when a high gloss image is formed.